Low alloy steel having good stress corrosion cracking resistance

Abstract

The present invention relates to low alloy steel and specifically to nickel-chrome-molybdenum steel. A low alloy steel having excellent stress corrosion cracking resistance containing C:</=0.40%, Si:</=0.15%, Mn:</=0.20%, P:</=0.010%, S:</=0.030%, Ni: 0.50 to 4.00%, Cr: 0.50 to 2.50%, Mo: 0.25 to 4.00% and V:</=0.30%, said Si, Mn and P being fulfilled with relationship of Si+Mn+20P</=0.30%, the remainder comprising Fe and unavoidable impurities, the prior austenite crystal grain size being in excess of 4 of ASTM crystal grain size number.

What is claimed is: 
     
       1. A low alloy austenitic steel having good stress corrosion cracking resistance consisting essentially of C:≦0.40%, Si:≦0.15%, Mn:≦0.60%, P:≦0.010%, S:≦0.030%, Ni: 0.50 to 4.00%, Cr: 0.50 to 2.50%, Mo: 0.25 to 4.00% and V:≦0.30% and further containing at least one element selected from the following (i) and (ii) groups: (i) At least one of Al, Ti, Nb, W, B or Ce: 0.001 to 0.50% in total   (ii) Sn: 0.003 to 0.015% the remainder being Fe and unavoidable impurities, the austenite crystal grain size thereof being in excess of 4 of ASTM crystal grain size number.     
     
     
       2. A low alloy austenitic steel having good stress corrosion craking resistance consisting essentially of c:≦0.40%, Si:≦0.15%, Mn:≦0.60%, P:≦0.010%, Si:≦0.030%, Ni: 0.50 to 4.00%, Cr: 0.50 to 2.50%, Mo: 0.25 to 4.00% and V:≦0.30% and further containing at least one element selected from the following (i) and (ii) groups consisting of: (i) At least one of Al, Ti, Nb, W, B or Ce: 0.001 to 0.50% in total   (ii) Sn: 0.003 to 0.015% said Si, Mn and P being fulfilled with the relationship of Si+Mn+20P≦0.75%, the remainder being Fe and unavoidable impurities, the austenite crystal grain size thereof being in excess of 4 of ASTM crystal grain size number.